The Magician is one, and acts outward; the High Priestess is two, and knows inward. She sits between two pillars, a veil behind her, a crescent moon at her feet, an unopened scroll in her lap. Everything in the picture says 'not yet revealed': the pillars are opposites, the veil hides what hasn't been seen, the scroll is knowledge not yet read. Two here is the boundary between inside and out — she sits at the door, going neither way.
Where you'll recognise it: strong intuition you can't justify, the sense that things aren't only what they appear, and the moments when you know the answer and haven't admitted it. This card is about receiving rather than acting: the world is telling you something — are you listening?
Running well, the High Priestess is the quietest and most accurate state: unhurried, unshowy, knowing when not to speak. Stuck, her problem is staying entirely inside — feeling everything and expressing nothing, deciding nothing; or treating intuition as a reason not to check. The scroll is meant to be read and the veil eventually lifted. She's only saying: not yet.